There are numerous industrial and commercial applications where it is desirable to control a flowing fluid with an inexpensive normally open non-electric valve, as opposed to the commonly employed normally closed solenoid type of valve. For example, small water purification systems using reverse osmosis membranes are useful in localities where the water quality is poor and conventional solenoid valve mechanisms tend to become clogged with mineral deposits. It is precisely in those locations, however, that electrical power supplies tend to be spotty and expensive, so that reliance on electrical power is prone to shut off the water even though the water mains are still under pressure. In such localities, cost also tends to be a major factor in equipment selection and operation, a consideration that is exacerbated by the fact that holding a common solenoid valve open uses electricity continuously, and the fact that specially designed non-electrical normally open valves are expensive.
Another situation in which inexpensive non-electric normally open valves are useful is one in which flammable or explosive liquids need to be conveyed in small, low-cost installations with little supervision and maintenance.